The unanimous decision Monday will also likely preserve the trademarked and controversial name of the Redskins, Washington’s NFL team, and help the Seattle band Thunderpussy trademark its name.

WASHINGTON — The Supreme Court extended trademark protection to words and names that may be offensive, ruling Monday that the First Amendment right to free speech allows an Asian-American band from Portland, Oregon, to call itself the Slants.

The law at issue denies federal trademark protection to messages that may disparage people, living or dead, along with “institutions, beliefs or national symbols.” The high court Monday struck down part of the 1946 federal law.

The justices said this provision violates “a bedrock First Amendment principle: Speech may not be banned on the ground that it expresses ideas that offend,” said Justice Samuel Alito Jr. He said trademarks are “private speech,” not the government speaking. And as such, the law may not punish words or expressions simply because they are offensive.

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“We have said time and time again that the ‘public expression of ideas may not be prohibited merely because the ideas are themselves offensive to some of their hearers,’ ” Alito said in the case of Matal v. Tam.

Slants founder Simon Tam tried to trademark the band name in 2011, but the U.S. Patent and Trademark Office denied the request on the ground that it disparages Asians.

The examiner cited dictionaries that defined “slants” or “slanteyes” as a derogatory or offensive term.

The Slants said they did not intend to disparage anyone. Instead, they said, they sought to adopt and reform a disparaging term about Asians, much…